Method for blast furnace operation



March 8, 1966 Filed April 27, 1965 L5. OXYGEN/LB. FUEL J. H. MENK ETAL3,239,331

METHOD FOR BLAST FURNACE OPERATION 2 Sheets-Sheet 1 RELATIONSHIP BETWEENHYDROCARBON FUELS AND OXYGEN 4 LOG Y .O32 X .76

4 6 B IO [2 l4 l6 I8 20 22 24 CARBON HYDROGEN RATIO INVENTORS JAMES H.MENK JOHN B.POWERS A TTORNEV March 8, 1966 J. H. MENK ETAL METHOD FORBLAST FURNACE OPERATION 2 Sheets-Sheet 2 Filed April 27, 1965RELATIONSHIP BETWEEN HYDROCARBON FUELS AND BLAST TEMPERATURE LOG Z xv XA LOG Z .O33X L3 CARBON- HYDROGEN RATTO INVENTORS JAM ES H. M EN K JOHNB. POWERS By mur A77'ORNEV United States Patent 3,239,331 METHOD FORBLAST FURNACE OPERATION James H. Menk, Mountainside, N.J., and John B.Powers,

Westport, Comm, assignors to Union Carbide Corporation, a corporation ofNew York Filed Apr. 27, 1965, Ser. No. 453,557 17 Claims. (Cl. 75-42)This application is a continuation-in-part of copending applicationSerial No. 264,863, filed March 13, 1963, in the name of J. H. Menk andJ. B. Powers.

This invention relates to a method for operating blast furnaces and,more particularly, to an improved method for operating blast furnaceswherein greater economics are achieved over a wide range of productionlevels.

In the production of iron from iron ores in the blast furnace, theconventional practice is to charge iron ore, coke and limestone into thefurnace. The coke is combusted by blast air preheated in the furnacestoves and then forced into the furnace through tuyeres to provide theheat and reducing gases required to smelt the iron oxides to iron. Theamount of coke needed is quite large, generally about 1400 or 1500pounds of coke for each ton of pig iron produced, and represents a largepart of the cost of the iron making operation.

The state of the art has advanced considerably through experience inregard to more economical operating practices. The operating region of ablast furnace is determined by physical and thermochemical laws thatgovern the transfer of heat and chemical energy required for thesmelting of the charge in the shaft and hearth of the furnace. Withother blast variables held constant, it has been found that the rate ofsmelting of a given ore, and hence the iron production rate, is directlyproportional to the rate at which coke and other fuels are oxidized inthe furnace, which in turn is a function of the rate at which blast airis supplied through the tuyeres. In the interest of securing greaterproduction from a furnace, and thereby securing a more economical rateof production by virtue of the proportionally larger base fordistribution of fixed capital and operating expenses, it has been commonpractice to achieve maximum production by driving the furnace with themaximum amount of blast air allowable within the limits of properfurnace operation.

The maximum blast rate is generally determined by the limits of blowerhead pressure, lifting of the charge in the stack, or entrainment offines in the top-gas exhausts. At the maximum blast rate permissiblewithin these restrictions, there is a maximum blast temperature limitdetermined by the capability of the furnaces blast stove system. In manyinstances, this temperature limit is imposed by the total heat transfercapacity of the stove rather than by allowable operating temperatures ofthe blast air conveying system, meaning that the pipes, bustles andtuyeres could handle blast air at a higher temperature if the stovescould supply it. To supply blast air at such higher temperatures, itwould be necessary to operate at wind rates lower than the maximumblower capaicty.

While increased production rates resulting from driving the furnace withmaximum blast rates are beneficial, the high blast temperaturesresulting from reduced wind rates will also greatly improve smeltingefficiency and economy of furnace operation. Generally, the higher theblast temperature which can be utilized, the lower the quantity of cokerequired per ton of iron produced. Since the cost of the metallurgicalcoke consumed normally represents 25 to 40 percent of the cost of a tonof iron, it is obviously desirable to reduce the coke requirements asmuch as possible for lowest cost operation. It can Patented Mar. 8, 1966be demonstrated theoretically and corroborated in practice that as theblast volume rate of a furnace is decreased, that the coke rate alsodecreases. This method of operation is termed slack wind blowing. Theunfortunate feature of a slack wind operating technique is that as theblast volume rate is reduced to affect coke savings, the furnaceproduction decreases proportionally, thus nullifying, and even wipingout the cost savings accruing from the lower coke fate. It has notgenerally been possible to combine the advantages of better thermalefficiency from slack wind blowing with the inherent cost savings whichresult from operating a facility at or greater than its maximum ratedproduction.

Another area in which blast furnace operating economies are sought is inregard to the substitution of cheaper hydrocarbon fuels such as naturalgas, fuel oil, and pulverized coal, for part of the normal cokerequirement of the furnace. Typically, coke reductions of to 300 poundsper ton of iron have been achieved by such auxiliary fuel additions. Thefurther substitution of hydrocarbon fuel for coke has been limited,however, by the inability to maintain proper furnace operation andefiiciency at the higher levels of fuel injection compared to resultsobtained at lower levels, thus restricting coke savings to theaforementioned 100 to 300 pounds per ton of iron.

It is the object of this invention to provide a more economical methodfor operating a blast furnace which method applies over a wide range ofproduction levels.

It is also an object of this invention to provide a method for operatingblast furnaces wherein the cost saving advantages of controlled blastvolume rates as well as savings resulting from use of hydrocarbon fueladditions are achieved at all levels of furnace production, i.e., atnormal capacity, at less than normal capacity, and in great excess ofnormal capacity.

The invention comprises a method for operating blast furnaces whereinthe furnace is charged with iron bearing materials, coke, and slaggingmaterials such as limestone, comprising determining a minimum flametemperature in the smelting zone for maximum smelting efiiciency,substituting for part of the coke auxiliary hydrocarbon fuels whileadding oxygen and blast heat in an amount sufficient to maintain theflame temperature at about its minimum level while increasing the rateof smelting, reducing the coke rate through the addition of theauxiliary fuels while the value of the resulting coke reduction is equalto or greater than the cost of supplying said auxiliary fuels andoxygen, and regulating the blast volume to give a desired ironproduction rate.

In the drawings:

FIG. 1 is a graphical representation of the equations showing the properrelationships of oxygen and fuel additions to a blast furnace;

FIG. 2 is a similar representation of the proper relationships of fueland blast temperature additions to a blast furnace.

As previously stated, the substitution of cheaper hydrocarbon fuels formore expensive coke has already resulted in savings of up to 100 to 300pounds of coke per ton of iron. The further substitution of largeramounts of such fuels as natural gas, fuel oil, or pulverized coal hasbeen restricted, however, by an inability to maintain proper furnaceconditions at the higher levels of fuel injection. One limitation on theamount of auxiliary fuels which can be substituted for coke is due tothe fact that these fuels do not supply as much heat on combustion inthe blast furnace as an equal weight of hot coke. When hydrocarbon fuelsare injected into the smelting zone of the furnace, they require addedthemochemical energy for their dissociation and so their combustion doesnot liberate enough heat to maintain the normal smelting zonetemperature. It is, therefore, necessary to make additional heatavailable in the blast furnace. This can be done by increased blastvolume or temperature, decreasing the blast moisture, or by oxygenenrichment of the blast air. Fuel injections into blast furnaces havebeen made along with one or more of the above listed heat providingmeans to compensate for the heat load put on the furnace by thehydrocarbon fuel. These processes have resulted in some coke savings.The coke reductions were not as great as could be expected and weregenerally linked to operation at higher production levels.

The amount of hydrocarbon fuel additions, and hence the amount of cokesavings, could be increased if better methods were available tocompensate for the reduced flame temperature caused by the fueladditions. Blast temperature control is limited by the stove capacity ofthe furnace which means that to obtain substantially increased blasttemperatures, blast volume must be reduced, and thus production rate issacrificed. Moisture control is of course limited. Oxygen enrichment, asWell as each of the above heat supplying means, can cause eitherundercompensation or excessive overcompensation of the flametemperatures. Improper use of any of these can cause such a deficit ofheat in the smelting zone as to ultimately result in freezing, or, onthe other hand, release such great amounts of heat as to cause excessivesmelting zone temperatures which lead to extremely rough stock descentand furnace hanging. The inability to cope with these factors and stillproduce cost savings at the higher levels of fuel injection has kept theamount of coke savings at the lower levels indicated before.

The operating limits of a blast furnace are dictated by physical andthermochemical laws that govern the transfer of heat and chemical energyrequired for the smelting of the charge. These laws establish a balanceamong the furnace charge ingredients, auxiliary fuels, enthalpy,oxidation capacity of the blast gas, etc. This balance must bemaintained within prescribed bounds to provide suitable smeltingconditions. Within these bounds there exist a number of operablecombinations that satisfy the physical constraints without regard toeconomics of raw materials supplied.

It has been found that to achieve the most eflicient operation of ablast furnace when injecting auxiliary fuels, the blast furnace shouldbe operated about the lower range of flame temperatures within thebroader operable flame temperature limits. Therefore, in order to derivemaximum benefits from the use of oxygen enrichment, blast temperatureincrease and hydrocarbon fuel injection, it is first desirable toestablish this range pf maximum smelting efliciency and minimum flametemperatures for the particular blast furnace and raw materialsinvolved. Maximum efiiciency in the economic sense results fromoperation in the lower range of flame temperature because it is cheaperto replace. as much coke as possible with lower cost hydrocarbon fuel,auxiliary hydrocarbon fuels tending to decrease flame temperature asdiscussed previously.

On a furnace without fuel injection, the normally considered optimumflame temperature can be approximated by a trial and error manipulationof the blast variables, volume, temperature, moisture content, etc., toachieve the lowest posible coke rate for a given burden and desiredlevel of iron production. This optimum flame temperature and minimumcoke rate will usually be found at the highest blast temperatureconsistent with smooth furnace operation. From this starting point amethod for approaching the minimum flame temperature more closelycomprises the following: Hydrocarbon fuels are added to the smeltingzone of the furnace in increments of say to pounds per ton of iron, andconcurrently the coke charged to the top of the furnace is reduced anequal amount. It is recognized that the amount of coke which can beremoved per unit hydrocarbon fuel atoms in the fuel.

addition is dependent on many factors, among them the type ofhydrocarbon fuel added, the amount of increased blast temperatureavailable, etc. However, for the purpose of establishing a startingpoint, replacement of coke can be initially made on a 1 for 1 weightbasis. The operator, by judging the temperature and quality of the ironcan then decide whether even greater replacement of fuel for coke can betolerated. For example, for a natural gas fuel with relatively highhydrogen content it may be possible to replace as much as two pounds ofcoke for each pound of gas added. For fuel oil or coal perhaps as muchas 1.5 pounds of coke can be removed per pound of fuel. The operatorstarting from the suggested 1 to 1 replacement of fuel for coke, andmodifying this according to iron quality and temperature, can thenproceed to add fuel and substract coke in increments,-

until the incremental coke reduction per unit incrementalfuel additionfalls off appreciably, to say or 50 percent of the initial ratio. Thesmelting conditions then existing represent approximately the minimumflame tem-- perature at which the furnace will operate properly at theavailable blast temperature.

When the minimum flame temperature has been established as outlined,hydrocarbon fuels are then added to the furnace and the coke rate isreduced, while oxygen enrichment of the blast, or increasing blasttemperatures are made, in such amounts that the minimum flametemperature is maintained and not overcompensated for norundercompensated.

It has been found that the proper amount of oxygen to be added or degreeof blast temperature increase needed to accompany any hydrocarbon fueladdition may be expressed as a function of the carbon-hydrogen atomicweight ratio of the fuel. In the drawings, graphs are shown which can beused to determine the amount of oxygen or blast temperature increaseneeded to ac-- company any hydrocarbon fuel injection.

Based on the graph of FIG. 1, the minimum amount of oxygen (Y) neededper pound of fuel addition is log Y=.042X-i-0.61 or Y=antilog(0.042X+0.61)

where X is the carbon-hydrogen atomic weight ratio of the hydrocarbonfuel added. The carbon-hydrogen atomic weight ratio, as used herein, isthe ratio of the weight of carbon atoms in the fuel to the weight ofhydrogen For example, the gaseous fuel methane will have acarbon-hydrogen weight ratio of 12 to 4X1 equal to 3. Where the additionis of more than one fuel, or a slurry of several fuels, such as oil andpul verized coal, then X is the weighted ratio of the combined carbon tohydrogen atomic weights. The maximum amount of oxygen which should beadded with the injection of a fuel having a carbon-hydrogen ratio X islog 10Y=-0.032X+0.76

On the semi-logarithmic chart of FIG. 1 the minimum oxygen additionneeded is Y=antilog (-0.042X +0.61) and the maximum oxygen addition thatshould be is Y=antilog (0.032X+0.76). The vertical offset between thesecurves represents the range of proper oxygen additions for any givencarbon-hydrogen ratio.

For any given furnace, the operator should select an oxygen-fueladdition ratio representing about the mid point of the indicated rangefor the particular fuel being injected, and then vary the oxygen-fueladdition ratio either higher or lower from this mid point, while stayingwithin the range, as is found necessary to maintain proper irontemperature and quality.

In regard to the case where blast temperature is increased along Withhydrocarbon fuel injections and diminishing coke rates, FIG. 2 shows achart from which can be determined the number of pounds of hydrocarbonfuels of a given carbon-hydrogen ratio (X) that can be added to afurnace for each 100 F. increase over the normal blast temperature usedin that furnace. For either a single fuel or a mixture of fuels having acombined carbon-hydrogen weighted ratio X, the maximum number of poundsof fuel (Z) per ton of iron which can be added for each 100 F. blasttemperature increase is g10 OI' Z=antilog (0.033X-I-L3) and the minimumnumber of pounds of fuel (Z) per ton of iron which should be added foreach 100 blast temperature increase is log Z= 0.032X+ 1.08

On the semi-logarithmic chart of FIG. 2 the maximum hydrocarbon fueladdition for each 100 F. blast temperature increase is Z=antilog(0.033X-|-1.3) and the minimum is Z=autilog (0.032X +1.08). The verticaloffset between these curves represents the range of proper fueladditions for a fuel having the given carbon-hydrogen ratio for each 100F. blast temperature increase.

For any given furnace, the operator should select a fuel addition per100 increase in blast temperature which is about the mid point in therange indicated for that particular fuel, and then vary the amount ofthe fuel addition per 100 temperature increase either higher or lowerfrom this mid point, while staying within the range, as is foundnecessary to maintain proper iron temperature and quality.

For common hydrocarbon fuels natural gas, oil, and pulverized coal thefollowing figures, based on the abovedescribed equations and typicalcarbon-hydrogen ranges for such fuels, can be used: in the case ofhydrocarbon fuel injection at constant blast temperature with oxygenenrichment, add 2.7 to 4.5 pounds of oxygen per pound of natural gas;for fuel oil, add 1.7 to 3.0 pounds of oxygen per pound of oil; forcoal, add 0.64 to 1.4 pounds of oxygen per pound of coal; when more thanone of these hydrocarbon fuels are to be simultaneously injected intothe furnace, then the amount of oxygen to be added is the sum of theoxygen requirements for each individual fuel addition.

Similarly, when common hydrocarbon fuels are to be substituted for cokewith an accompanying blast temperature increase, the amount of suchfuels which may be added for each 100 F. blast temperature increase isas follows: for natural gas, 16 to 27 pounds of natural gas per ton ofiron; for fuel oil, 20 to 40 pounds of oil per ton of iron; and forpulverized coal, 50 to 90 pounds of coal per ton of iron; when more thanone of these hydrocarbon fuels are to be simultaneously injected intothe furnace, then the amount of each fuel which may be added isproportioned according to the ranges given above, i.e., on the basis ofthe portion of the total blast temperature increase assigned to overcomethe heat load on the furnace created by that fuel. Additionally, whenoxygen enrichment and blast temperature increases are both utilized theproper fuel additions are determined by combining the amount of fuelwhich can be added because of the amount of oxygen enrichment with theamount of fuel that can be added because of the degree of blasttemperature increase.

It is seen from the above discussions that cheaper hydrocarbon fuels maybe substituted for part of the normal furnace coke requirement providedthat either oxygen is added to the furnace or blast temperatures areincreased. The greatest economies are achieved, however, with oxygenenrichment of the blast and blast temperature increases. Whenhydrocarbon fuels and oxygen are added to the furnace in the ratiostaught herein, the hydrocarbon fuels will replace part of the furnacecoke requirement, while the oxygen not only counteracts the chillingeffect of the hydrocarbon fuel and maintains optimum smeltingefliciency, but also increases the burning rate of the coke. Whileincreased coke burning rates cause increased production, it is possible,because of the oxygen injections, to control production by regulatingthe blast volume or wind rate to the furnace, i.e., the blast volumerate can be adjusted to either maintain normal production or to operateat substantially below normal or above normal, with substantial cokesavings at all levels. Additionally, as blast volumes are cut back, theresulting blast temperature increases allow the use of greater amountsof hydrocarbon fuels, thereby further reducing coke rates.

It is an important aspect of this invention that substantial cokesavings can be made essentially independent of the furnace productionrate whereby the economies of reduced coke rates can be achieved at anydesired production level. As an illustration, consider the case Where itis desired to maintain normal production rate on a blast furnace, but toachieve greater economies in use of raw materials. The blast furnacewill have a certain production, coke rate, blast temperature and volume,and blast moisture content. Before making the supplementary fueladditions, it is generally desirable to start out with optimum flametemperature conditions in the smelting zone. Generally the furnace willbe operating with the highest-blast temperature consistent with smoothoperation which would result in optimum flame temperature for a furnacewithout fuel injection. The minimum flame temperature range can then beapproached starting from this point by the incremental fuel additionprocedure previously outlined.

Starting from this minimum flame temperature point, further auxiliaryfuel additions are made. The graphs can be used for any hydrocarbon fuelor mixture of fuels by determining the carbon-hydrogen ratio of the fuelor of the mixture, and then adding the indicated amount of oxygen orblast temperature increase for each increment of fuel addition. As anexample, for fuel oil with a C-H ratio of 8.8 to 1, from 1.7 to 3.0pounds of oxygen per pound of oil should be injected to maintain theflame temperature and drive the smelting rate faster. When compensatingwith blast temperature increases, 24 to 40 pounds of oil per F. increaseshould be used. These relationships hold for constant blast moisture. Itis recognized that blast moisture can be used to control flametemperature in both situations of increasing blast temperature or inincreasing oxygen content. For example, it is known that a quantity ofmoisture can be added to the blast with an associated amount of oxygenenrichment. If hydrocarbon fuels were added to a furnace already havingthis moisture-oxygen injection, then additional oxygen would be addedwith the fuel according to the relationships set forth herein. In otherwords, the method of this invention relates oxygen enrichment and blasttemperature enrichment to hydrocarbon fuel additions; if moisturecontrol or other pertinent operating factors are varied, then any oxygenenrichment or blast temperature increases associated with thesevariables are not to be considered in regared to the hydrocarbon fueladdition.

The auxiliary fuel additions are then made along with the indicatedoxygen additions and blast temperature increases, or both, while thecoke rate is reduced. In actual practice the coke reductions may be madein the form of increasing the burden to coke ratio. As a starting pointcoke reductions can be made on the basis of the substitution of a unitweight of hydrocarbon fuel for a unit weight of coke. It is to be notedthat variations from this one to one substitution are to be expecteddepending on the type of hydrocarbon fuel used. The actual substitutionof hydrocarbon fuels for coke is to be made by the blast furnaceoperator according to the principles of proper furnace operation and thedirections set forth above in regard to the incremental fuel injectionmethod for determining the minimum flame temperature. The extent towhich hydrocarbon fuels, oxygen and blast temperature can be profitablysubstituted for coke depends on the relative cost of these materials.Generally, the substitutions should be made as long as the value of thecoke saving is equal to or greater than the cost of supplying thehydrocarbon fuel and oxygen necessary to produce that coke saving. Therelative costs of coke, various hydrocarbon fuels and oxygen will varyfrom area to area, but it will be generally the case that thecombination of hydrocarbon fuels and oxygen will allow savings withreduced coke rates of up to 40 to 60 percent of normal cokerequirements.

Since the addition of oxygen has the effect of increasing the smeltingrate and, hence the amount of iron produced, the wind rate should now becutback to reduce the iron production rate from the level which wouldresult from the use of the given amount of oxygen back to the normalproduction rate. The amount of wind rate cutback should be such as tosupply to the furnace only about enough total oxygen as is needed tocombust with the amount of coke and auxiliary fuels needed for thedesired iron production rate. It is important to note that this windrate reduction is not the same as slack wind blowing where productionrates fall off sharply and the coke rate per ton of metal drops onlyslightly. Here much greater coke reductions are achieved, while theproduction rate may remain the same or be dropped drastically, to say,50 percent of normal.

The wind rate reductions here are not the same as the reductions inblast volume made in conjunction with prior art oxygen enrichmentmethods. There the wind rate would be reduced by the amount of airequivalent in oxidizing power to the amount of pure oxygen supplied. Ineffect, this is a reduction in blast volume of the excess, unneedednitrogen content of the air. This slight reduction in blast volume gavesome increase in blast temperature, but the resulting coke reductionswere not of the order involved in this process.

The substantial reductions in wind rate made possible by the use ofoxygen additions according to the process of this invention allow theattainment of higher blast temperatures, which, in turn, allow thesubstitution of additional hydrocarbon fuels for the more expensivecoke.

In the actual practice of the invention, oxygen and fuel are added whilethe coke rate is reduced. The oxygen-fuel proportioned additions willcause an increase in the production rate. The furnace operator willobserve this increased production rate and cut back the wind rate to thefurnace so as to reduce the production rate to the desired level.

If it were desired to operate the furnace with a lower than normalcapacity, then the blast volume would be cut back still further so as toprovide only enough total oxygen to combust the coke and auxiliary fuelsneeded to produce the desired lower iron production rate.

When a greater than normal iron production is required, the auxiliaryfuels and oxygen are added as above, but the blast volume reductions arenot so great as with normal production rates. Oxygen enrichment canproduce much more iron at the same or even lower blast volumes. Forexample, furnaces can be made to produce 150 percent of their normalcapacity with substantial coke reductions by following the teachings ofthis invention without exceeding the blower capacity of the furnace.

As an example of the application of the invention to a particularfurnace, take the case of a blast furnace having a normal, present dayproduction rate of 800 tons per day. This furnace consumed coke at therate of 1310 pounds per ton of iron and used 1140 cu. ft. of natural gasper ton of metal produced. The blast temperature was 1300 F. with volumeof 45,000 c.f.m. The blast was air, i.e., contained 21 percent by volumeoxygen, and had 3 grains per cubic foot moisture content.

To meet a hypothetical reduction in steel demand, the blast furnaceproduction was ordered cut back to 500 tons per day. An economicalmethod of operation comprised eliminating the natural gas injection andinjecting 335 pounds per ton of pulverized coal with an accompanyingoxygen addition. The blast volume was cut back to 25,000 c.f.m., and thepercent oxygen in the blast was 22.5 percent by volume. The moisturecontent was the same, 3 grains per cubic foot. The blast temperature wasraised to 1600 F. because of the blast volume reduction. The resultingcoke rate was only 790 pounds per ton of metal produced.

When normal production Was required, the process of this inventionprovided the following method of operation: the production rate wasstill 800 tons per day, but the coke rate was reduced from 1310 poundsper ton to 900 pounds per ton by adding 290 pounds of pulverized coalper ton and 2380 cu. ft. of natural gas per ton along with oxygen. Theblast temperature was 1600 F. with an oxygen content of 25.7 percent byvolume in a 35,000 c.f.m. blast and the same moisture content, 3 grainsper cu. ft.

When the desired furnace production rate was 1000 tons per day, 400pounds of pulverized coal per ton and 1400 cu. ft. of natural gas perton were added to the furnace. The blast volume was 46,500 c.f.m. at ablast temperature of 1,450 P. and a moisture content of 3 grains per cu.ft. The oxygen content of the blast was 25.3 percent by volume. The cokerate was only 900 pounds per ton of metal produced.

If such increases in blast temperature were not available, then byincreasing the oxygen content according to the principles of thisinvention, then the desired increase in production could be achievedwith the blast temperatures actually available.

It is clear from the above description and examples, that substantialcost reductions are attainable by substituting lower cost hydrocarbonfuels with oxygen and increased blast temperatures for part of thenormal coke requirement according to the process of this invention. Forany hydrocarbon fuel or mixture of fuels, oxygen and blast temperatureincreases can be added in the proper quantities to maintain maximumsmelting efiiciency While realizing substantial savings in coke.Furthermore, maximum smelting efficiency and low coke rates can beachieved independent of furnace production rates.

What is claimed is:

1. A method for the operation of a blast furnace wherein iron-containingmaterials, coke, and slagging materials are charged, comprisingsubstituting for part of the coke an auxiliary hydrocarbon fuel whileadding oxygen to the blast furnace, the minimum oxygen addition beingaccording to the equation Y=antilog (0.042X +0.61), and the maximumoxygen addition according to the equation Y=antilog (0.032X +0.76),where Y is oxygen addition in pounds per pound of fuel and X is thecarbon-hydrogen ratio of the fuel, reducing the coke rate through theaddition of the auxiliary fuels, and operating the blast furnace at adesired production rate by decreasing the wind rate from the normal windrate for desired production rates equal to and less than the normal rateand increasing the wind rate for production rates substantially greaterthan the normal rate.

2. A method for the operation of a blast furnace wherein iron-containingmaterials, coke, and slagging materials .are charged, comprisingsubstituting for part of the coke an auxiliary hydrocarbon fuel whileadding blast heat to the furnace, the maximum number of pounds of fueladded being according to the equation Z=antilog (0.033X-1.3), and theminimum number of pounds of fuel according to the equation Z: antilog(0.032X+1.08), where Z is the number of pounds of fuel added per 100 F.blast temperature increase per ton of iron produced, and where X is thecarbon-hydrogen ratio of the fuel, reducing the coke rate through theaddition of the auxiliary fuels, and reducing the blast volume to thefurnace to achieve blast temperature increases and to give a desiredproduction rate.

3. A method for the operation of a blast furnace wherein iron-containingmaterials, coke, and slagging materials are charged, comprisingsubstituting for part of the coke an auxiliary hydrocarbon fuel whileadding oxygen and heat to the blast furnace, the minimum oxygen additionbeing according to the equation Y: antilog (0.042X+0.6 1)

the maximum oxygen addition according to the equation Y=antilog (0.032X+0.76), where Y is the oxygen addition in pounds per pound of fuel addedwith oxygen enrichment, and X is the carbon-hydrogen ratio of the fuel,the heat added to the furnace as increases in blast temperatureaccompanied by additional hydrocarbon fuel additions, the maximum numberof pounds of additional fuel being according to the equation Z=antilog(0.033X+ 1.3)

and the minimum number of pounds of fuel according to the equationZ=antilog (0.032X +1.08), where Z is the number of pounds of fuel per100 F. blast temperature increase per ton of iron produced, and X is thecarbon- .hydrogen ratio of the fuel, reducing the coke rate through theaddition of the auxiliary fuels, and operating the blast furnace at adesired production rate by decreasing the wind rate from theinormal windrate for desired production rates equal to and less than the normal rateand increasing the wind rate for production rates substantially greaterthan the normal rate.

4. A method for the operation of a blast furnace Wherein ironcontainingmaterials, coke, and slagging materials are charged, comprising settinga minimum flame temperature in the furnace, and then substituting forpart of the coke an auxiliary hydrocarbon fuel while adding oxygen tothe blast furnace, the minimum oxygen adition being according to theequation Y antilog (-0.042X+O.6l)

and the maximum oxygen addition according to the equation Y antilog(-0.032X +0.76), where Y is oxygen addition in pounds per pound of fueland X is the carbonhydrogen ratio of the fuel, reducing the coke ratethrough the addition of auxiliary fuels, and operating the blast furnaceat a desired production rate by decreasing the wind rate from the normalwind rate for desired production rates equal to and less than the normalrate and increasing the wind rate for production rates substantiallygreater than the normal rate.

5. A method for the operation of a blast furnace wherein iron-containingmaterials, coke, and slagging materials are charged, comprising settingthe minimum flame temperature in the furnace for maximum smeltingefficiency by first operating the furnace under normal conditions andmaking supplemental incremental additions of hydrocarbon fuels whilemaking incremental reductions in the coke rate until the incrementalcoke reduction per incremental hydrocarbon fuel addition falls offsubstantially, and thereupon substituting additional hydrocarbon fuelfor part of the coke requirement while adding oxygen to the blastfurnace, the minimum oxygen addition being according to the equationY=antilog (-0.042X-|-0.61), and the maximum oxygen addition according tothe equation Y=antilog (0.032X+0.76), where Y is oxygen addition inpounds per pound of fuel and X is the carbon-hydrogen ratio of the fuel,reducing the coke rate through the addition of auxiliary fuels, andoperating the blast furnace at a desired production rate by decreasingthe wind rate from the normal wind rate for desired production ratesequal to and less than the normal rate and increasing the wind rate forproduction rates substantially greater than the normal rate.

6. A method for the operation of a blast furnace where- 1.0 iniron-containing materials, coke, and slagging materials are charged,comprising setting a minimum flame temperature in the furnace, and thensubstituting for part of the coke an auxiliary hydrocarbon fuel whileadding oxygen and blast heat to the blast furnace, the minimum oxygenaddition being according to the equation and the maximum oxygen additionaccording to the equation Y=antilog (0.032X+0.76), where Y is the oxygenaddition in pounds per pound of fuel added with oxygen enrichment, and Xis the carbon-hydrogen ratio of the fuel, the heat added to the furnaceas increases in blast temperature over normal with additionalhydrocarbon fuel addition, the maximum number of pounds of fuel beingaccording to the equation Z =antilog (0.033X+ 1.3), and the minimumnumber of pounds of fuel according to the equation Z==antilog(0.032X+1.08), where Z is the number of pounds of fuel per F. blasttemperature increase per ton of iron produced, and X is thecarbon-hydrogen ratio of the fuel, reducing the coke rate through theaddition of the auxiliary fuels, and reducing the blast volume to thefurnace to give a desired production rate and blast temperatureincrease.

7. A method for the operation of a blast furnace wherein iron-containingmaterials, coke, and slagging materials are charged, comprising settingthe minimum flame temperature in the furnace for maximum smeltingefficiency by first operating the furnace under normal conditions andthen making incremental additions of hydrocarbon fuels while makingincremental reductions in the coke rate until the incremental coke rateper incremental fuel addition falls off substantially, and substitutingadditional hydrocarbon fuel for part of the coke fuel while addingoxygen and blast heat to the blast furnace, the minimum oxygen additionbeing according to the equation Y=antilog (0.042X+0.6 1)

and the maximum oxygen addition according to the equation Y=antilog(0.032X+0.76) where Y is the oxygen addition in pounds per pound of fueladded with oxygen enrichment, and X is the carbon-hydrogen ratio of thefuel, the heat added to the furnace as increases in blast temperatureaccompanied by additional hydrocarbon fuel addition, the maximum numberof pounds of fuel being according to the equation Z=antilog (0.033X+1.3), and the minimum number of pounds of fuel according to theequation Z :antilog (0.032X +1.08), Where Z is the number of pounds offuel per 100 F. blast temperature increase per ton of iron produced, andX is the carbonhydrogen ratio of the fuel, reducing the coke ratethrough the addition of the auxiliary fuels, and operating the blastfurnace at a desired production rate and economy by decreasing the windrate from the normal wind rate for desired production rates equal to andless than the normal production rate and increasing the wind rate forproduction rates substantially greater than the normal rate.

8. A method for the operation of a blast furnace wherein iron-containingmaterials, coke, and slagging materials are charged, comprising settinga minimum flame temperature in the furnace, and then substituting forpart of the coke an auxiliary hydrocarbon fuel while adding oxygen tothe blast furnace, the minimum oxygen addition being according to theequation Y antilog (0.032X+0.76), where Y is the oxygen addition inpounds per pound of fuel and X is the carbon-hydrogen ratio of the fuel,reducing the coke rate through the addition of the auxiliary fuels,while the value of the coke saved is at least equal to the cost ofsupplying the auxiliary fuels and oxygen, and reducing the Wind ratefrom the normal wind rate with air so that the total mass of oxygenentering in the blast is less than that of the normal Wind rate withair.

9. A method for the operation of a blast furnace wherein iron-containingmaterials, coke, and slagging materials are charged, comprising settinga minimum flame temperature in the furnace, and then substituting forpart of the coke an auxiliary hydrocarbon fuel while adding oxygen andblast heat to the blast furnace, the minimum oxygen addition beingaccording to the equation Y=antilog (0.042X +0.61), and the maximumoxygen addition according to the equation Y=antilog (-0.032X+0.76),where Y is the oxygen addition in pounds per pound of fuel added withoxygen enrichment, and X is the carbonhydrogen ratio of the fuel, theheat added to the furnace as increases in blast temperature over normalwith additional hydrocarbon fuel addition, the maximum number of poundsof fuel added being according to the equation Z=antilog (0.033X+1.3),and the minimum number of pounds of fuel according to the equationZ=antilog (0.032X-|-l.08), where Z is the number of pounds of fuel per100 F. blast temperature increase per ton of iron produced, and X is thecarbon-hydrogen ratio of the fuel, reducing the coke rate through theaddition of the auxiliary fuels, and reducing the wind rate from thenormal wind rate with air so that the total mass of oxygen entering inthe blast is less than that of the normal wind rate With air.

10. A method for the operation at less than normal capacity of a blastfurnace wherein iron-containing materials, coke, and slagging materialsare charged, comprising setting a minimum flame temperature in thefurnace, and then substituting for part of the coke an auxiliaryhydrocarbon fuel While adding oxygen, and blast heat to the blastfurnace, the minimum oxygen addition being according to the equationY=antilog (0.042X+0.6l), and the maximum oxygen addition according tothe equation Y=antilog (0.032X +0.76), where Y is the oxygen additionper pound of fuel added with oxygen enrichment, and X is thecarbon-hydrocarbon ratio of the fuel, the heat being added to thefurnace as increases in blast temperature over normal with additionalhydrocarbon fuel addition, the maximum number of pounds of fuel addedbeing according to the equation Z=antilog (0.033X +1.3), and the minimumnumber of pounds of fuel according to the equation Z=antilog (0.032X+1.08), where Z is the number of pounds of fuel per 100 F. blasttemperature increase per ton of iron produced, and X is thecarbon-hydrogen ratio of the fuel, reducing the coke rate through theaddition of the auxiliary fuels, and reducing the wind rate from thenormal Wind rate with air so that the total mass of oxygen entering inthe blast is less than that of the normal wind rate with air and is onlysufficient to supply the furnace requirements at the desired lower rateproduction.

11. A method for the more economical operation of a blast furnace atabout its normal capacity, wherein ironcontaining materials, coke, andslagging materials are charged, comprising determining a minimum flametemperature in the furnace, and then substituting for part of the cokean auxiliary hydrocarbon fuel while adding oxygen and blast heat to theblast furnace, the minimum oxygen addition being according to theequation Y=antilog (-0.042X +0.61), and the maximum oxygen additionaccording to the equation Y=antilog (0.032X+0.76)

where Y is the oxygen addition in pounds per pound of fuel added withoxygen enrichment, and X is the carbonhydrocarbon ratio of the fuel, theheat being added to the furnace as increases in blast temperature overnormal with additional hydrocrabon fuel addition, the maximum number ofpounds of fuel added being according to the equation Z antilog(0.033X+1.3), and the minimum number of pounds of fuel according to theequation Z antilog (0.032X+l.08), where Z is the number of pounds offuel per 100 F. blast temperature increased per ton of iron produced,and X is the carbon-hydrogen ratio of the fuel, reducing the coke ratethrough the addition of the auxiliary fuels, and reducing the wind ratefrom the normal wind rate with air so that the total mass 12 of oxygenentering in the blast is less than that of the normal wind rate with airand is only sufficient to supply the furnace requirements at the givennormal production rate.

12. A method for the operation of a blast furnace at an increased rateof production wherein iron-containing materials, coke, and slaggingmaterials are charged, comprising ilame temperature in the furnace,substituting for part of the coke an auxiliary hydrocrabon fuel whileadding oxygen and blast heat to the blast furnace, the minimum oxygenaddition being according to the equation Y=antilog (0.042X+0.6l), andthe maximum oxygen addition according to the equation Y: antilog(-0.032X+0.76)

where Y is the oxygen addition in pounds per pound of fuel added withoxygen enrichment, and X is the carbonhydrocarbon ratio of the fuel, theheat being added to the furnace as increases in blast temperature overnormal with additional hydrocarbon fuel addition, the maximum number ofpounds of fuel added being according to the equation Z=antilog(0.033X+1.3), and the minimum number of pounds of fuel according to theequation Z=antilog (0.032X+1.08), where Z is the number of pounds offuel per F. blast temperature increased per ton of iron produced, and Xis the carbon-hydrogen ratio of the fuel, reducing the coke rate throughthe addition of the auxiliary fuels, and regulating the wind rate to thefurnace so that the total mass of oxygen entering in the blast is onlysuflicient to supply the furnace requirements at the desired higherproduction rate.

13. A process for the operation of a blast furnace whereiniron-containing materials, coke in a normal amount of about 1400-1500pounds of coke per ton of iron, and slagging materials are charged intothe furnace, comprising substituting for part of the coke an auxiliaryhydrocarbon fuel while adding oxygen and heat to the blast furnace, theminimum oxygen addition being according to the equation Y=antilog(0.042X+0.6l), and the maximum oxygen addition according to the equationY=antilog (.032X+0.76), Where Y is the oxygen addition in pounds perpound of fuel added with oxygen enrichment, and X is the carbon-hydrogenratio of the fuel, the heat added to the furnace as increases in blasttemperature over normal with accompanying hydrocarbon fuel additions,the maximum number of pounds of fuel added being according to theequation Z=antilog (0.033X+1.3), and the minimum number of pounds offuel according to the equation Z=antilog (0.032X+l.08), where Z is thenumber of pounds of fuel per 100 F. blast temperature increase per tonof iron produced, and X is the carbon-hydrogen ratio of the fuel,reducing the coke rate through the addition of the auxiliary fuels, and,as a lower limit, to a coke rate of 700 to 850 pounds of coke per ton ofiron, and operating the blast furnace at a desired production rate andeconomy by decreasing the wind rate from the normal wind rate fordesired production rates equal to and less than the normal productionrate and increasing the wind rate for production rates substantiallygreater than the normal rate.

14. A method for the operation of a blast furnace whereiniron-containing materials, coke, and slagging material are charged,comprising substituting for part of the coke an auxiliary hydrocarbonfuel selected from the group consisting of natural gas, oil and coalwhile adding oxygen to the blast furnace, the amount of oxygen added tothe furnace per pound of fuel added being from 2.7 to 4.5 pounds fornatural gas, from 1.7 to 3.0 pounds for oil, from 0.64 to 1.4 pounds forcoal, and in amounts proportional to these when more than one fuel isselected, reducing the coke rate through the addition of the auxiliaryfuels, and operating the blast furnace at a desired production rate bydecreasing the wind rate from the normal wind rate for desiredproduction rates equal to and less than the normal production rate andincreasing 13 the wind rate for production rates substantially greaterthan the normal rate.

15. A method for the operation of a blast furnace whereiniron-containing materials, coke, and slagging materials are charged,comprising substituting for part of the coke auxiliary hydrocarbon fuelsselected from the group consisting of natural gas, oil, and pulverizedcoal While adding heat to the furnace through increases in the blasttemperature, the amount of fuel added for each 100 F. increase in blasttemperature per ton of iron being from 16 to 27 pounds of natural gas,from 20 to pounds of oil, from to pounds of coal, and in amountsproportional to these when more than one fuel is selected, reducing thecoke rate through the addition of the auxiliary fuels, and reducing theblast volume to achieve blast temperature increases and give a desiredlevel of production.

16. A method for operating a blass furnace wherein iron-containingmaterials, coke, and slagging materials are charged, comprisingsubstituting for part or" the coke auxiliary hydrocarbon fuels selectedfrom the group consisting of natural gas, oil, and pulverized coal whileadding oxygen and heat to the furnace, the amount of oxygen added perpound of fuel being from 2.7 to 4.5 pounds for natural gas, from 1.7 to3.0 pounds for oil, from 0.64 to 1.4 pounds for coal, and in amountsproportional to these when more than one fuel is selected, the heatadded to the furnace being in the form of blast temperature increasesaccompanied by additional hydrocarbon fuel additions, the amount ofadditional fuel added for each F. increase in blast temperature per tonof iron being from 16 to 27 pounds of natural gas, from 20 to 40 poundsof oil, from 50 to 90 pounds of coal, and in amounts proportional tothese when more than one additional fuel is selected, reducing the cokerate through the addition of the auxiliary hydrocarbon fuels, andoperating the blast furnace at a desired production rate by decreasingthe wind rate from the normal wind rate for desired production ratesequal to and less than the normal production rate and increasing theWind rate for production rates substantially greater than the normalrate.

17. A method for operating a blast furnace wherein iron-containingmaterials, coke, and slagging materials are charged, comprisingdetermining a minimum flame temperature in the furnace, and thensubstituting for part of the coke auxiliary hydrocarbon fuels selectedfrom the group consisting of natural gas, oil, and pulverized coal whileadding oxygen and heat to the furnace, the amount of oxygen added perpound of fuel being from 2.7 to 4.5 pounds for natural gas, from 1.7 to3.0 pound for oil, from 0.64 to 1.4 pounds for coal, and in amountsproportional to these when more than one fuel is selected, the heatadded to the furnace being in the form of blast temperature increasesaccompanied by additional hydrocarbon fuel additions, the amount ofadditional fuel added for each 100 F. increase in blast temperature perton of iron being from 16 to 27 pounds of natural gas, from 20 to 40pounds of oil, from 50 to 90 pounds of coal, and in amounts proportionalto these when more than one additional fuel is selected, reducing thecoke rate through the addition of the auxiliary hydrocarbon fuels, andregulating the blast volume to the furnace to give a desired productionlevel.

References Cited by the Examiner FOREIGN PATENTS 872,062 7/1961 GreatBritain.

OTHER REFERENCES Blast Furnace, Coke Oven and Raw Materials Prooeedings,published by AIMME, vol. 19, 1960, pages 23 8- 253; vol. 21, 1962, pp.15-41.

References Cited by the Applicant UNITED STATES PATENTS 2,727,81612/1955 Raick. 2,735,758 2/1956 Strassburger. 3,062,640 11/1962 Agarwalet al.

OTHER REFERENCES Blast Furnace Performance With Injection at theTuyeres, J. M. Ridgion, Journal of the Iron and Steel Institute, October1961, pages to 143.

DAVID L. RECK, Primary Examiner.

1. A METHOD FOR THE OPERATION OF A BLAST FURNACE WHEREIN IRON-CONTAININGMATERIALS, COKE, AND SLAGGING MATERIALS ARE CHARGED COMPRISINGSUBSTITUTING FOR PART OF THE COKE AN AUXILIARY HYDROCARBON FUEL WHILEADDING OXYGEN TO THE BLAST FURNACE, THE MINIMUM OXYGEN ADDITION BEINGACCORDING TO THE EQUATION Y=ANTILOG (-0.042X +0.61), AND THE MAXIMUMOXYGEN ADDITION ACCORDING TO THE EQUATION Y=ANTILOG (-0.032X+0.76),WHERE Y IS OXYGEN ADDITION IN POUNDS PER POUND OF FUEL AND X IS THECARBON-HYUDROGEN RATIO OF THE FUEL, REDUCING THE COKE RATE THROUGH THEADDITION OF THE AUXILIARY FUELS, AND OPERATING THE BLAST FURNACE AT ADESIRED PRODUCTION RATE BY DECREASING THE WIND RATE FROM THE NORMAL WINDRATE FOR DESIRED PRODUCTION RATES EQUAL TO AND LESS THAN THE NORMAL RATEAND INCREASING THE WIND RATE FOR PRODUCTION RATES SUBSTANTIALLY GREATERTHAN THE NORMAL RATE.